Need help with FFI on 32 vs 64-bit versions of Love2d 11.2

[ivan]

Hello. I am working on a wrapper library for Steamworks v1.44 using just FFI. The library uses just pure FFI without custom-built binaries. This allows for easy maintenance and upgrades in the future. The source code is available here:
https://github.com/2dengine/sworks-ffi
The library works good, but I am having trouble with the callbacks mechanism behind Sworks. I managed to get it working on Love2D 64-bit, but I can't get it to work on 32-bit versions of Love2D. Note that the callbacks mechanism requires C++ which makes things messy but not impossible. Also note that I have tried to take struct packing into account between platforms. I use "jit.off(func, true)" for the function that triggers the Sworks callbacks.
On 32-bit versions of Love2D, I get a crash after a callback is triggered (see vt:Run1 and vt:Run2 which are supposed to be virtual functions)
Would appreciate any feedback as to why this works fine on 64-bit versions of Love2D but fails on 32-bit. I don't know much about FFI so any help is greatly appreciated. Thanks!

Further reading:
https://garry.tv/2016/11/01/steamworks-sdk/

[grump]

Have you tried to run it on a "real" 32 bit OS? Maybe it's a pointer size issue. Just guessing though.

It's probably not relevant to your problem, but I'm pretty sure the cast from <event> to <event>* is not required.

Code: Select all

local ffi = require('ffi')

ffi.cdef("typedef struct Blah { int i; };")

local b = ffi.new("struct Blah")
local p = ffi.cast("struct Blah*", b)

assert(b == p) -- true

ffi.new already returns a pointer to the allocated object.

Code: Select all

ffi.cdef([[
typedef unsigned char uint8;
typedef unsigned char uint8;
typedef signed char int8;
typedef short int16;
...

uint8 is defined twice. These are already defined, btw. They are named uint8_t, int16_t, etc.

[ivan]

Hey Grump,
Thank you so much for taking a look at this. I'm not very good with C or FFI so any help is greatly appreciated.

Have you tried to run it on a "real" 32 bit OS? Maybe it's a pointer size issue. Just guessing though.

Have not tried that yet, everything works great, except for Steamworks' callbacks mechanism.
Also, note that the 64-bit binaries work fine even with the callbacks enabled.

ffi.new already returns a pointer to the allocated object.

I'm trying to cast a void pointer there, so without the asterisk * I get:

Code: Select all

Error: utils/avatar/sworks/api.lua:697: bad argument #1 to 'cast' (invalid C type)

Note that events are C++ objects with inheritance and virtual functions.
Not really sure how to handle this otherwise.

uint8 is defined twice.

Good catch there, this should be fixed as of today!

[grump]

I'm trying to cast a void pointer there

I see. Please disregard my comment, I wasn't reading the code properly.

[raidho36]

I'm asking because you haven't specified: are you using 32 bit DLLs with 32 bit executables?

[ivan]

True, the code is hacky because we are faking C++ which is clearly unsupported by FFI.

I'm asking because you haven't specified: are you using 32 bit DLLs with 32 bit executables?

Yes, 32 bit binaries (vanilla love2d and sworks) on a 64 bit OS.

[pgimeno]

This looks dodgy to me:

Code: Select all

typedef unsigned char uint8;
typedef signed char int8;
typedef short int16;
typedef unsigned short uint16;
typedef int int32;
typedef unsigned int uint32;
typedef long long int64;
typedef unsigned long long uint64;

Maybe try

Code: Select all

typedef uint8_t uint8;
typedef int8_t int8;
typedef int16_t int16;
typedef uint16_t uint16;
typedef int32_t int32;
typedef uint32_t uint32;
typedef int64_t int64;
typedef uint64_t uint64;

[ivan]

I tried your version and it still crashes at the same point: virtual function call at vt:Run1
Btw, I didn't come up with that definition, it comes from "steam_api_flat.h"